1. Field of the Invention
The present invention relates to an automobile seat capable of easing, when an automotive vehicle has come into a rear-end collision, an impact to a lumbar part of a seat occupant.
2. Description of the Related Art
When a rear-end collision has occurred, an impact applied to an automobile body is transmitted to a human body via a seat and may injure an occupant of the seat.
Japanese Laid-Open Patent Publication No. 2000-118279 discloses a seat back frame structure for an automobile seat wherein a horizontal frame having a generally L-shaped cross section extends between lower end portions of opposite side frames. In this seat back frame structure, a plurality of horizontally extending stiffening beads or ridges are formed on a bottom wall and a vertical wall of the horizontal frame, while two vertically extending energy absorbing beads or ridges are formed on the vertical wall of the horizontal frame. The energy absorbing beads are deformed when an impact force is applied thereto in an event of a rear-end collision.
Japanese Laid-Open Patent Publication No. 2001-145538 discloses another seat back frame structure wherein a lower portion of a seat back frame has a impact absorbing portion formed by partially pressing the lower portion into a planar shape so as to have a strength lower than other portions. The strength of the impact absorbing portion is so set that the impact absorbing portion may be deformed when an impact force is applied thereto in an event of, for example, a front-end collision.
The seat back frame structure as disclosed in the above-described patent publications is intended to absorb impact inputted from outside by deforming a portion of the seat back frame, but cannot ensure an amount of deformation sufficient to absorb large impact energy and, hence, there is still room for improvement.